3-D TV disparities said to cause physical, mental strain

PORTLAND, Ore. — Visual disparities in 3-D TV images can cause physical strain in viewers, according to recent research at the University of California at Berkeley.

While proper viewing conditions can help avoid most problems--dark room, central seat far from the screen--3-D cinematographers also need to follow careful rules or risk making people sick, researchers said.

A stereo viewing chair that rotates was designed by UC-Berkeley researchers to allow manipulation of visual and vestibular cues to self-motion and body orientation.

The debate over 3-D TV heated up earlier this week when Samsung issued a warning about possible health effects.

Even if the physical strains of 3-D are avoided, other disparities can cause mental strain akin to vertigo, according to other investigators at the University of Washington. "If [cinematographers] confined 3-D to animations, then there wouldn't be a problem [since] the brain doesn't have the same expectations about cartoons," said Aris Silzars, founder of Northern Lights, a display technology consultancy (Sammamish, Wash.)

For the emerging crop of 3-D movies that incorporate real-world scenery, movie makers have one extra job beyond those of previous animations: Minimizing the so-called vergence-accommodation conflict.

The conflict arises from the fact that 3-D displays often cause distortions in perceived 3-D structure compared with the percepts of the real scenes the displays depict.

"The only thing we have any data on is what we call the vergence-accommodation conflict, which our lab has shown really does cause fatigue, discomfort, eye strain and headache in some cases," said professor Martin Banks, who led the research into 3-D eye strain at the UC-Berkeley, which was funded by the National Institutes of Health.

According to Banks, when viewers direct their eyes at nearby objects or scenes, their gaze converges. When they gaze into the distance they, diverge, or what optometrists call "vergence." Conversely, focusing the eye muscles to bring something into sharp focus is called "accommodation."

In the real world, vergence and accommodation are synched to the same distance, but in the world of 3-D stereoscopic glasses decouple the two, forcing the brain to cope with a disparity between the vergence and accommodation distances.

"Normally the distance to which you converge your eye and accommodate your focus are the same, so understandably your brain has coupled these together," Banks said. "The problem is a stereo or 3-D display breaks this coupling, and the reason why is that the disparity between the images that are being presented to the two eyes might specify something behind the screen or in front of the screen--and in those two cases you have to converge your eyes to a different distance than the screen, but you still have to accommodate the screen because that is where the light comes from."

The Berkeley researchers have performed two studies that reached the same conclusion: 3-D TV induces a vergence-accommodation disparity in the brain that manifests itself in a statistically significant number of people as fatigue, discomfort, eye strain and headaches. So far, test subjects have been between 18 and 30, but Banks plans to test 50-year-olds to determine whether they are immune to the vergence-accommodation conflict, as he suspects, since older eyes do not focus as well.